The present invention relates to an apparatus and a method for recording and/or reproducing information in relation to an optical information recording medium by using a holography.
In the past, there have been an optical information recording and/or reproducing apparatus that records information in an information recording area (information recording surface) and/or reproduces the information from the area, of a reflection-based optical information recording medium (optical disk), such as CD (Compact Disk), DVD (Digital Versatile Disk), etc.
Recently, it is also possible to realize commercially available reflection-based disks having a recording density as large as 50 GB in consumer use, in accordance with the specifications of Blu-ray disk (hereinafter, referred to as BD) using a blue-violet semiconductor laser, HD DVD (High Definition DVD), etc. On the contrary, it is also desirable to realize an optical disk having a large storage capacity as large as 100 GB to 1 TB mostly equal to the storage capacity of HDD (Hard Disk Drive).
However, for a purpose of realizing the foregoing ultra-high density by the optical disk, it is necessary to realize a new storage technique different from the existing high density technique obtained from the traditional approach such that a wavelength is made short and NA of an objective lens is made high. Consequently, a holographic recording technique has attracted attention in these years such that digital information is recorded by using a holography. According to the holographic recording technique, it is effective to record and reproduce information in large volume and high speed since two-dimensional information can be recorded and reproduced simultaneously by one hologram, and plural pieces of page data can be written over the same area.
As an example of the holographic recording technique indicated above, there is an angle multiplex recording system, in which a signal beam is focused on a holographic optical disk (hereinafter, referred to as a hologram disk) by a lens, at the same time, a reference beam of a parallel pencil is irradiated thereon and interfered to record a hologram, and each piece of page data is displayed on a spatial light modulator to perform a multiple recording while an incidence angle of the reference beam toward the hologram disk is changed. The foregoing technique has been disclosed in JP-A-2004-272268.
WO2004-102542 has also proposed a holographic recording technique using a shift multiplexing, in which a beam from pixels inside one spatial light modulator is regarded as a signal beam, and a beam from pixels of orbicular zone shape outside the spatial light modulator is regarded as a reference beam, both the foregoing beams are then focused on the hologram disk by the same lens used for both the beams, and the signal beam and reference beam are made interference with each other in the vicinity at a focal plane of the lens to thereby record a hologram.